Accompanying the development and popularization of electrically rich vehicles, such as hybrid vehicles, electric vehicles, and fuel cell vehicles, are also trends toward increasing complexity and size of in-vehicle power circuits. For example, hybrid vehicles have increasingly complex configurations including a drive battery, a system battery, a plug-in external power circuit, a DC/DC converter for supplying DC power of the drive battery to a drive motor, a DC/AC converter for converting DC power of the drive battery to AC power, a DC/DC converter for supplying DC power of the drive battery to electric power steering (EPS), a DC/DC converter for supplying DC power of the drive battery to accessories, and so forth.
Accordingly, multi-port power supplies comprising a plurality of inputs and outputs in a single circuit are being developed. Multi-port power supplies offer the miniaturization of power supply circuits through the sharing of wiring, semiconductor devices, and so forth.
JP 2011-193713 A discloses a configuration where electric power conversion is possible between selected multiple ports in an electric power conversion circuit comprising four ports. More specifically, a circuit configuration is disclosed coupling a bidirectional non-isolated chopper circuit and a bidirectional isolated converter utilizing magnetically coupled reactors and transformer.
However, in a multi-port circuit, core loss of the transformer during light loading becomes dominant and controlling this becomes essential for further improving fuel economy of hybrid vehicles. Although reducing the maximum magnetic flux density is effective in suppressing core loss of transformers, circulating current develops if only the duty is modulated and an increase in loss occurs outside the transformer.